The general goal of this project is to provide a psychophysical description of the sensitivity of normal, intact skin to common chemicals. Building upon the results obtained during the prior funding period, the project will continue to study the perceptual characteristics (in humans) of what is typically referred to as the common chemical sense. In addition, the focus of the project will begin to move from simple descriptive studies toward investigations of sensory coding in the nociceptive and thermal senses using chemical stimuli as probes. These aims will be pursued in three types of psychophysical analyses: (1) studies of the basic perceptual characteristics of sensorially-active compounds, which will provide information about the range and complexity of perceptual experiences that can be evoked by topical irritants; (2) studies of the spatial and temporal interactions among chemical stimuli, and between chemical stimuli and other cutaneous stimuli, which will provide data on phenomena such as summation, inhibition, "sensitization" and "desensitization;" and (3) studies of chemical mixtures and the interactions between simultaneously-applied chemical and thermal stimulation, which are designed to provide clues to the sensory processes that underlie the perception of complex nociceptive and thermal sensations on the skin.